Effects of biochar from gasifier stove and effluent from biodigester on growth of maize in acid and fertile soils

Pham Thi Luyen, Duong Nguyen Khang and T R Preston*

Abstract

The study was conducted at the experimental farm of Nong Lam
University, Ho Chi Minh City from October 2010 to May 2011. A maize biotest was
used to evaluate three factors: biochar (at levels 0, 2, 4 and 6%), two kind of
soils (acid and fertile soil), biodigester effluent (with and without). There
were in total 16 treatments with 4 repetitions, arranged in a complete
randomized block design.

The combination of biochar and effluent increased the height
of the maize (from 48 to 157 cm) and the biomass yield (from 27 to 114 g/plant)
compared with the control treatment. There were improvements in soil pH after
addition of biochar and in mineral status after application of effluent.

Introduction

The recent interest in
biochar (Lehman 2005) as a soil amender has its origins in the discovery of
Terra Preta by Sombroek (1966, cited by Glaser 2007). Terra preta is an artificial, human-made soil, which originated before
the arrival of Europeans in South America (http://en.wikipedia.org/wiki/Terra_preta).
Indigenous people made the soil by applying charcoal, bone, and manure to the
otherwise relatively infertile Amazonian soil.

Biochar in the modern
context is produced by the combustion of organic matter in a low oxygen
environment. It is rich in minerals including potassium, phosphorus, calcium,
zinc, and manganese. But the most important ingredient is carbon, giving the
dark colour. Biochar is not oxidized by soil micro-organisms, compared with
traditional forms of charcoal which eventually are completely broken down when
applied to soils. The chemical structure of biochar is characterized by the
presence of poly-condensed aromatic moieties, giving prolonged stability against
microbial degradation and oxidation, and high nutrient retention (Glaser 2007).

It has been proposed that
biochar can reduce the effects of global warming since the carbon that it
contains is resistant to attack by soil micro-organisms thus acting as a “sink”
for carbon (Lehman et al 2006). According to these authors, about 10% of the
total global fossil fuel carbon emissions could be sequestered in soils as
biochar. Debate has taken place concerning potential negative effects on food
production if land is diverted to growing and harvesting biomass solely to
produce “biochar”. Another issue relates to the problems involved in transport
of low density biomass for production of biochar in large scale centralized
processing facilities.

A recent approach that seeks to avoid these negative
aspects of biochar is the use of small scale biomass gasifier stoves that
combine the advantages of a clean-burning fuel, that avoids the pollution and
health hazards from open fires, and at the same time produces biochar as a
by-product (Olivier 2011).

The results from applying
biochar to soils have been quite dramatic, especially on acid soils when the
biochar has been used in conjunction with organic fertilizer in the form of
biodigester effluent (Rodríguez et al 2009).

The present study aims to evaluate the use of biochar as a
soil amender in acid and fertile soils used to grow maize.

Hypothesis

The beneficial effects of
biochar on maize growth will be greater in acid soils and there will be a
positive synergism when biochar is combined with effluent from biodigesters
charged with animal excreta.

Experimental design

Sixteen treatments were
compared in a 4*2*2 factorial arrangement with 4 replications. The factors were:

Biochar: Four levels of biochar (0, 2, 4 and
6%) added to the soils in the plastic bags

Soil type: Acid soil or fertile soil

Biodigester effluent: With or without effluent
at 50 kg N/ha over 35 days

Biochar

The biochar was the solid
residue from an up-draft gasifier stove charged with rice husks as fuel
(Photo 2).

Photo 2a.
The updraft gasifier stove, charged with rice husks prior to being
ignited with paper

Photo 2b.
The biochar from the updraft gasifier stove

Biodigester effluent

Effluent was collected from
a plug-flow biodigester constructed with High Density Polyethylene (HPDE) (Photo
3) located in a commercial pig farm.

Photo 3.
The plug-flow biodigester
made from High Density Polyethylene (HDPE) located in a commercial
pig farm in Binh Duong province

Experimental soils

Two types of soil were used
in the experiment. The acid soil (pH 4.5) was taken from the top 10cm in an
un-shaded area in the Nong Lam University campus. The almost neutral soil (pH
6.4 ) was taken from the top 10cm in the same area but under trees that provided
shade.

Photo 4.
The acid soil

Photo 5.
Close to neutral soil

.

Maize seeds

These were of a local
variety. Three seeds were placed in each bag. After germination, two seedlings
were removed to leave only one plant for the experimental growth period of 42
days.

Measurements

At 7, 14, 21, 28, 35 and 42
days after seeding the height of the maize was measured at the tip of the
highest leaf. At the end of the growth period of 42 days, the complete plant
was removed from the bag and the aerial part separated from the roots which were
washed free of soil. Both fractions were weighed. The pH of the soil was
measured with a digital pH meter at the time of harvesting the maize. The ash
content of the biochar was determined by incineration at 700°C
(AOAC 1990). Soil analysis was according to AOAC (1990) as follows:
physical characteristics by density gauge; total nitrogen (N) by Kejdah'; total
phosphorus (P2O5) by colorimetry; total potassium (as K2O)
by flame photometry.

Statistical analyses

The data were analysed by the General Linear Model of the ANOVA program in the
Minitab (2000) Software. Sources of variation were: level of biochar, soil type,
effluent, interaction biochar*effluent and error.

Results

The two soils were very different in physical and chemical
properties (Table 1).The fertile soil had higher proportions of clay and silt
and lower content of sand; and was higher in N and K2O than in the
acid soil. The high pH of the biochar is a common feature of biochar produced
from both downdraft gasifiers and updraft gasifier stoves (9.5 and 9.8,
respectively according to Sokchea and Preston 2011). The residual ash was 45%
(DM basis) which is lower than the value of 77% recorded by Southavong et al
(2012) for biochar derived from stove gasification of rice hulls.

Table 1.
Characteristics of the soils

Acid

Fertile

pH

4.5

6.5

Chemical
composition, %

N

0.007

0.176

P2O5

0.08

0.07

K­2O

0.09

0.18

Physical
composition, %

Clay

27.8

43.4

Silt

5.32

8.76

Sand

66.9

47.9

There
was a linear increase in the height of the maize and in biomass yield with
increase in biochar up to 4% in the soil with no further increase with 6% of
biochar (Tables 2 and 3; Figures 1 - 4). Application of biodigester effluent
increased the height of the maize and biomass yield, at all levels of
application of biochar. There were tendencies for increases in yield of leaf and
above ground biomass on the fertile compared with the acid soil. These
differences were significant for weights of stem, root and total biomass.

Table 2.
Mean values for effects of level of biochar on growth of maize over
42 days

Level
of biochar, % in soil

SEM

P

0

2

4

6

Height, cm

76.8

85.9

116

123

6.0

<0.001

Biomass,
g/plant

Leaf

23.9

34.6

54.1

52.5

4.1

<0.001

Stem

38.7

54.5

93.4

94.3

6.5

<0.001

Leaf+stem

62.5

89.1

148

147

10.5

<0.001

Root

21.7

40.4

76.9

81.0

5.1

<0.001

Total

84.2

129

224

228

15.5

<0.001

Table 3.
Mean values for effects of soil type and biodigester effluent on
growth of maize over 42 days

Soil type

Effluent

Acid

Fertile

P

0

50 kg N/ha

P

SEM

Height, cm

105

96.4

0.200

72.0

129

<0.001

4.22

Biomass,
g/plant

Leaf

37.6

45.0

0.086

34.4

48.1

0.002

4.22

Stem

63.7

76.7

0.040

53.8

86.6

<0.001

4.57

Leaf+stem

101

122

0.055

88.2

135

<0.001

7.70

Root

49.4

60.6

0.030

43.5

66.5

<0.001

3.62

Total

151

182

<0.001

132

201

<0.001

11.0

Figure 1.
Effect of biochar and biodigester effluent on height of maize after
42 days

Figure 2.
Effect of biochar and biodigester effluent on green biomass (leaf +
stem) of maize after 42 days

Figure 3.
Effect of biochar and biodigester effluent on root biomass of maize
after 42 days

Figure 4.
Effect
of biochar and biodigester effluent on total biomass of maize after
42 days

Figure 5.
Effect of soil type on nutrient status of the soil at the end of
the 42 day growth trial

Figure 6.
Effect of effluent on nutrient status of the soil at the end of the
42 day growth trial

The beneficial effects of the biochar on growth of the
maize confirm earlier reports on use of biochar from a downdraft gasifier (Rodríguez
et al 2007) and updraft gasifier stove (Sokchea et al 2011). Contrary to the
findings of Rodríguez et al (2007), responses to biochar application tended to
be greater on the fertile soil than on the acid soil.

There were no residual effects on soil levels of N and K2O
due to application of biochar; however, levels of P2O5
were lower in the soils that received biochar (Table 4). As expected, the
fertile soil had higher levels of macro-nutrients than the acid soil, and there
were positive effects on soil nutrient status from application of biodigester
effluent.

Table 4.
Effect of
biochar on nutrient status of the soil at the end of the 42 day
growth trial

Level of biochar, %

0

2

4

6

SEM

P

N

0.0448

0.0308

0.0308

0.0245

0.0089

0.46

P2O5

0.0703a

0.0515b

0.0515b

0.0443b

0.0037

0.004

K2O

0.1033

0.0918

0.0825

0.0828

0.0044

0.23

Table 5.
Effect of soil type and biodigester effluent on nutrient status of
the soil at the end of the 42 day growth trial

Type of soil

Effluent, kg N/ha

Acid

Fertile

P

0

50

P

SEM

N

0.0084

0.0570

<0.001

0.0179

0.0475

<0.001

0.00628

P2O5

0.0476

0.0611

<0.001

0.0426

0.0661

0.005

0.00264

K2O

0.0724

0.1078

<0.001

0.0571

0.1230

<0.001

0.00310

Conclusions

There was a linear increase in maize biomass yield with increasing levels of
biochar up to 4% in the soil with no further increase with 6%.

Application of biodigester effluent increased biomass yield, at all levels
of application of biochar.

There was a greater response to biochar and to effluent application on yield
of biomass on the fertile compared with the acid soil.

Acknowledgments

The authors gratefully acknowledge the support
for this research received from the MEKARN program financed by Sida.